Thin-film transistors (TFTs) are used as switching elements or drive elements in active-matrix display devices, such as liquid-crystal display devices using liquid crystals or organic light-emitting diode (OLED) display devices using organic electro-luminescence (EL).
In recent years, regarding such display devices, there have been increased demands for pixel increase, area increase, and thickness reduction. Therefore, a TFT substrate having TFTs arranged in a matrix has technical aims of thinning each functional layer in the TFT substrate, reducing loss of electrodes and/or lines, and increasing a withstand voltage at an interlayer insulating film.
Patent Literature (PTL) 1 discloses a semiconductor device in which an alloy layer including a chemical element, which has an oxidation-reduction potential greater than that of copper, is disposed between a copper line and an insulating barrier film. This structure prevents oxidation of the copper line, thereby reducing an inter-line short circuit caused by copper oxides, withstand voltage reduction, and migration occurrence.